The invention relates to an electrical system for road vehicles and specifically the relationship between the vehicle""s electrical system and drive-train for controlling torque, power generation, and engine start-up.
Commercial vehicles such as semi-trucks, garbage haulers, buses and the like, often incorporate a retarder as a way to reduce the vehicle""s velocity without having to utilize friction brakes every time the vehicle is required to slow. Use of a retarder would therefore be a way to extend the useful life of a vehicle""s brakes and avoid frequent and costly brake maintenance.
The power supply for these retarder devices can come from several sources. Some retarders operate by controlling the intake and exhaust valves of an engine; some by restricting engine exhaust; while other retarders are designed to utilize hydraulic power, magnetic or electromagnetic interaction. All retarders function to absorb or dissipate the kinetic energy associated with a moving vehicle.
In this specification, retardation is defined as the use of an electromagnetic retarder to slow a vehicle.
For electromagnetic retarders, two methods are known in the prior art for exciting its magnetic field:
One method uses the vehicle""s battery and alternator, as a power source. As illustrated in FIG. 2, retarder 30 competes with the rest of the vehicle loads for available power. During retardation, which occurs for example when traveling downhill, the engine is operating at a lower RPM. For this situation, the output of alternator 22 is insufficient to maintain the battery fully-charged. Also, retardation causes depletion of the battery charge.
The second method uses permanent magnets instead of a field winding. In this configuration, there is no demand placed upon the vehicle battery and alternator for retardation. However, the torque produced by retardation is limited primarily to either a full ON or full OFF condition. Alternatively, a costly rotor displacement can be incorporated, which would provide the ability to vary the retardation torque.
Besides electromagnetic retardation, it is well known in the prior art to employ hydraulic retardation as a means for assisting vehicular braking.
The invention is best described as an electromagnetic retarder system for use with motorized vehicles. Additional functions can comprise the retarder system, which can be adapted to include one or a combination of the following: 1) a brushless DC alternator; 2) a brushless DC starter; 3) a passive/active damper that replaces the vehicle""s flywheel; 4) a transmission-synchronizing inertia brake; and, 5) a booster to offset the lag associated with using a turbocharger. A retarder system incorporating one or more of these functions can be collectively referred to as an Integrated Retarder And Accessory Device package (IRAAD). The IRAAD is explained below and has also been described in a previous patent application bearing Ser. No. 09/914,284.
The purpose of this application is to introduce two improvements that may be incorporated as part of an IRAAD. The first improvement is directed to a combination hydraulic-electromagnetic retarder and the second is directed to the use of a PMG in cooperation with a gear-box running off of the drive-train.
As disclosed in the application bearing Ser. No. 09/914,284, incorporated herein by reference, the housing which contains the retarder system may be integrated with the engine or with the transmission. While the engine is operating, it produces torque on the drive shaft for powering the transmission. When required, the retarder produces retardation torque, or negative torque, to reduce the velocity of a vehicle.
The retarder system can be positioned either at the input or the output of the transmission. Positioning is determined by the desired application, as each location has its own advantages.
For example, a retarder system placed at the output of a transmission can be made small and lightweight by providing it with a high speed shaft. However, at this position, the retarder system could not be an effective starter or generator because it rotates only when the transmission is engaged by the clutch or other torque link.
Conversely, a retarder system located at the input of a transmission, while large, may take advantage of gear ratios obtained from downshifting, to produce an even greater torque. Also, when the retarder rotor assembly, which will be discussed in detail below, is positioned between the engine and transmission, its function as a generator is unimpaired, as rotation occurs as long as the engine is running. Finally, because the rotor assembly of the retarder system is coupled directly to the crankshaft, the device can be used as a starter. For these stated reasons, the retarder system is preferably positioned between engine and transmission. Also, for this configuration, it is preferred that the induction ring, sometimes referred to as the retarder drum, be adapted for a coolant to pass through so that it can be connected to the vehicle""s existing cooling system (i.e. radiator) for dissipating the heat generated during retardation.
The invention comprises an electromagnetic retarder connected along the drive-shaft to an exciter generator. A permanent magnet generator (PMG) is drivingly coupled to the drive shaft. It can be located about the drive shaft but it is not directly connected to either the retarder or exciter generator in the physical sense although output from the PMG will be used for the exciter generator. At least one rectifier is positioned between and hard-wired to the field winding and exciter rotor. In the preferred embodiment, the field winding, the rectifier and the rotors of the exciter and PMG are collectively referred to as the retarder rotor assembly.
Positioned about the rotor assembly is a housing which can be integrated with either the engine or transmission housing, or as a separate housing. This housing preferably comprises the induction ring, and the stators of the exciter generator and PMG. Therefore, the retarder, exciter generator and PMG each have relatively rotatable elements, the stationary retarder induction ring and stators of the exciter generator and PMG, and their respective rotatable elements, the field winding and exciter rotor and PM rotor which rotate when the drive train is operable.
The exciter generator allows for brushless operation, while the PMG is referred to as xe2x80x9cself-excitedxe2x80x9d because its rotor is coupled to the vehicle""s drive-shaft and will produce current so long as the drive-shaft is rotating.
The electromagnetic retarder operates by energization of the rotating field winding of the rotor assembly to interact with a stationary induction ring to produce torque, which, together with drive-shaft rotation, generates power. Therefore, both of the retarder elements, the field winding and the induction ring are in surrounding relation to the main drive shaft.
It is important to note that, although torque may exist between the field winding of the rotor assembly and the induction ring even at a standstill due to magnetic attraction, for torque to be produced according to the invention, there must exist relative motion between the PMG rotor and stator. In other words, the field winding requires energization by an electric current which is created as a result of the output produced by the PMG.
This allows the PMG to convert mechanical power to the electrical energy required to energize the exciter generator and ultimately the field winding of the rotor assembly. Since the PMG will produce electricity whenever the drive-shaft is rotating, it is necessary to use a regulator to regulate the level of current reaching the exciter stator. Operation of the regulator would depend upon the type of external signal received. In addition, a power conditioning unit (PCU) is required to condition the alternating current (AC) produced by the PMG into direct current (DC).
The invention will operate equally as well if the induction ring is made to rotate, and the magnetic field is held stationary.
In addition to furnishing the electrical energy to power the exciter generator, the PMG can also be used for charging the vehicle""s battery; thus eliminating the need for an alternator. Further, the power flow through the PCU is partially reversible so that the battery can be used to motorize the PMG; thus eliminating the need for a starter.
Also, the inertia produced by the rotor assembly can effectively replace the engine flywheel. Controlled pulsing of the retarder in opposition to engine positive torque pulsations can achieve active torque damping. It is also possible to use the PMG as a motor and controllably pulse it in opposition to the engine""s negative torque pulsations to achieve a similar result, but with a higher net positive torque resulting.
Finally, it becomes possible to use the PMG as a motor to provide positive torque to the drive train, when a power boost is required. This power boost would be beneficial to compensate for the lag commonly encountered with a turbocharged system. The duration and amplitude of the boost would be limited by the capacity and state of charge of the battery. Because the PMG functions as a motor in some conditions and as a generator in other instances, the PMG can be referred to as a motor/generator.
Although the invention uses standard electromagnetic principles, i.e. a field interacting with an armature, it further provides the advantage of self-excitation, while retaining the controllability associated with field windings. This is accomplished by using an exciter generator in combination with a PMG on the same shaft and preferably within the same housing.
The invention has thus far taught an electromagnetic retarder by itself and in combination with one or more of four other functions. However, the principles discussed herein can also be applied without using a retarder in combination.
For example, a PMG configured with its rotor coupled to the drive-shaft and its stator thereabout can generate sufficient current to serve as an alternative to an alternator. Also, the vehicle starter can be replaced by utilizing the PMG as a brushless starter when an angular rotary position indicator is provided and an inverter is used to direct current from the vehicle""s battery.
Additional configurations can be obtained by combining the different functions mentioned above.
The invention provides the following advantages over the prior art:
The retarder system is self-excited in that it requires no energy from the vehicle""s battery or alternator. The battery therefore, will not be drained during the retardation cycle. The electrical power required to excite the retarder is generated by a PMG which converts mechanical energy from the rotating drive-shaft, into usable electricity.
The retarder system can be adapted so that the PMG is utilized to furnish electricity to charge the vehicle""s battery as well as providing electricity for the retarder""s operation; thus eliminating the need for an alternator.
The retarder system can also be adapted so that the battery can supply power to the PMG in a xe2x80x9cstarting modexe2x80x9d via a start inverter; thus eliminating the need for a starter. Also, with the engine running, the PMG can be made to compensate for turbocharging xe2x80x9clagxe2x80x9d by boosting the system with motive power.
The retarder system can also be adapted for use as an active/passive damper. The inertia developed by the rotor acts as a passive damper which can replace the flywheel. The retarder system can also employ active damping. The advantage of active damping is that mechanical stresses can be reduced, and thereby extend the life of the transmission, differential, and other drive train components.
The retarder system can also be adapted to replace the inertia brake commonly used in transmissions to aid in synchronizing gears while downshifting. The inertia brake is often expensive and requires the addition to the transmission of an extra power take off (PTO), consisting of at least a pair of gears.
Improved fuel efficiency will result from a reduction in overall vehicular weight. The prior art starter, which is a parasitic load as soon as the engine is started, is eliminated. The energy which would have been wasted as a parasitic load, is now available for other load purposes.
The retarder system results in improved reliability because: a) the number of component parts is reduced, b) the life of the transmission and other drive line components is extended because of a smoothing out of torque pulsations by the active damper, and, c) battery life can be extended because controlled starts minimize current surges encountered with normal, brush-type starters. Power management reduces the magnitude of power drain and extends the life of the battery.
For my purposes, I define hydraulic fluid as any fluid with the right combination of lubricity, viscosity, specific heat, specific gravity, electrical resistivity, high and low temperature characteristics, etc. that allows it to accomplish its intended use. This may end up being a light oil such as brake fluid, synthetic such as turbine oil, or heavier grades such as transmission fluid or engine oil. In any case, selection would be governed by the application.
As earlier described in my specification, the mass of the retarder electro-magnetic field replaces the mass of the engine flywheel, thus becoming a xe2x80x9cpassivexe2x80x9d damper. However, when the requirements for retardation torque are high, the rotor must be enlarged. The torque requirements may sometimes result in a rotor design exhibiting inertia that exceeds that of the original flywheel. Such a rotor design would detract from vehicle performance during acceleration. This is mathematically represented by the formula:
T=Ixcex1
Where:
T is Torque
I is Inertia
xcex1 is Angular acceleration.
In short, a large electromagnetic retarder can have a detrimental effect on vehicle acceleration and fuel efficiency. However, it is possible to design a retarder in accordance with my invention to obviate this negative effect. The design change would essentially modify the magnetic retarder into a hydraulic-electromagnetic retarder hybrid.
This modification consists of designing an electromagnetic retarder with a rotor mass and diameter that result in an inertia which is close to that of the original flywheel. The balance of the retardation torque required by the vehicle is obtained by allowing the rotor of the electromagnetic retarder to thrash through hydraulic fluid. The saliency of the rotor poles would thus emulate a hydraulic turbine and contribute substantially to the overall torque. This is accomplished by pumping under pressure a liquid such as hydraulic fluid into the retarder cavity at the time retardation is required.
Preferably, the retarder would be designed so that when the retarder cavity is empty, it matches the designed inertia of the flywheel it replaces. The torque furnished by the electromagnetic section would thus be sufficient for the driver""s purposes under most circumstances. Should additional retardation or faster deceleration be required, the electromagnetic torque can be supplemented by selectively closing the coolant drain passage and allowing it to fill the cavity surrounding the salient pole rotor. By proportionally varying the hydraulic fluid pressure, any rate of deceleration may be maintained.
Hydraulic flow into and out of the cavity is accomplished by a fluid circuit having an inline pump which can be operated either by operable connection to the drivetrain or powered by an electronic source. A control valve such as a solenoid valve is operably coupled to the fluid circuit and controls the flow of hydraulic fluid out of the cavity. The control valve is electronically connected to control unit which is also controls the electromagnetic retardation. This electronic circuit means determines the additional necessary torque to be provided hydraulically, what the desired level of hydraulic fluid within the cavity should be and controls the control valve accordingly.
Again, when retardation is demanded, the cavity of the hydraulic-electromagnetic retarder is filled under pressure with fluid to supplement the electromagnetic retardation without affecting inertia. The purpose is to minimize inertia imposed on the engine, and enhance acceleration and efficiency.
An advantage of my hydraulic-electromagnetic retarder hybrid is the combining of two different methods of retardation into one design to enhance performance over what could be achieved from either a hydraulic retarder or electromagnetic retarder of the same size.
Another advantage is that since hydraulic fluid is more efficient as a heat transfer medium than air, it can be used as a heat sink for the electromagnetic losses; and thereby transfer heat produced in the rotor as a result of friction and magnetic excitation more efficiently than standard electromagnetic retarders to the induction drum.
Since the power that a PMG produces is directly proportional to the rotational speed of the rotor relative to the stator, it is possible, rather than having the PMG directly connected to the drive-train, to have it operate on another shaft operatively connected to the drive-train by the use of a gear train.
For example, using a gear ratio of 4:1, a PMG of a certain size, coupled to the gear train is capable of generating 4 times the power than if it were directly coupled to the drive-train. It is then possible to use a smaller sized PMG when used with the appropriate gear train.
One advantage is that a smaller PMG is necessary to obtain the same output as a PMG located on the drive train.
Another advantage is that the PMG can be located in a separate housing separate from the retarder housing; or, it can be included within the same housing. Vehicular design or spacing considerations may prefer the PMG and gear box be located separate from the retarder housing. Because of the PMG location flexibility, the size of the retarder housing can be adapted to the application.
Still another advantage is that with the position of the PMG located away from the retarder housing, it is possible for the PMG to be replaced with a larger or smaller unit to suit the needs of the user.